Elastic-fluid turbine



Oct. 14, 1 941. R. P KRQON 2,258,773

ELAsTIc-FLUIp TURBINE Filed April 2, 1941 wrrNEssr-:s: F, 4 mvENToR www'C1' v RfNou'rEKRooN.

ATTO' 'EY a Curtis stage, and.'in general.

Patented Oct. 14, 1941.

UNITED .STATES PATENT lOFFICE 2,258,713 Reinout Prfdrtmh'more, Pa.,assigner to Westinghouse Electric d: Manufacturing Company, EastPittsburgh, Pa., a corporation of Pennsylvania Application April 2,1941, Serial No. 386,442

'Cl3ims. j (Cl. 253-39) The invention relates to stages oi.' elastic uidturbines, and it has for an object to resist effectively the inducementof blade vibration because of non-uniform flow of elastic uid issuingfrom nozzle or vane passages.

Tests have shown, not only that the invention is eiective for thepurpose indicated, but also that it is particularly desirable to employit where the pressure ratio across a stage is relatively high, theelastic iluid ow disturbances inducing blade vibration increasing as thevelocity and the pressure ratio increase and such disturbancesincreasing quite rapidly whenthe acoustic velocity is exceeded.Accordingly, a further object of the invention is to provide a stage ofthe highpressure ratio type and embracing vanes and blades, particularlyshort blades, and it has for an object to connect the blades together ingroups and to provide such relation of .nozzle or vane pitch, bladepitch, and the number of blades connected together in each group thatblade vibration, due to irregularities in flow caused by the l presenceof vanes, is eiectively resisted.

These and other objects are effected Vby the invention as will beapparent from the following description and claims taken in connectionwith the accompanying drawing forming a part of this application, inwhich:

Figs. 1 and 2 are diagrammatic views showing cooperating nozzles andblade groups:

Fig. 3 is a fragmentary view showing blade groups; and

Fig. 4 is a diagrammatic view. i

Referring to Figs. 1 and 4, the iiow of elastic fluid issuing from thevane or nozzle passages l0 is not uniform because oi' the wakesoccurring in the iiow behind each stationary vanel l. In Fig. 4, thisnon-uniform flow condition is diagrammatically shown, there being wakes,disturbances, .or reduced velocity zones a back of each vane Il andjoined by zones b o! more unifor it to travel from one nozzle to thenext.- vWhile this capability of non-uniformity of iow to restricted 50induce blade vibration is necessarily near the inlet end of the turbine,may come within the above frequency range. In Fig. 4, the top curveindicates the condition of dangerous blade vibration where a blade goesthrough one vibration cycle while traveling a distance equal the nozzlepitch p.

In accordance with the present invention, the blades I2 of the rstmoving row of an initial stage are connected byshroud elements i3 toform blade groups, at I4. In Fig. 1, showing an initial Curtis stage ofthe high-pressure ratio type, both the iirst and second moving rows ofblades are connected together in such groups;

l are similarly connected together in groups. The

number of blades connected in a group is such that the combined eect onall the blades in the group does not involve any exciting forces ofdangerous frequencies.. The blade pitch.' nozzle or vane pitch, andnumber of blades connected together in each group are so .arranged thatthe destructive forces fon the individual blades balance each other.Balancing is secured when the nozzle pitch, the blade pitch, andthenumber of blades in each group have the following relation P-:Pq where pis'the nozzle pitch, in. the blade pitch, n, the number of bladesconnected together in m is the number of vane passages covered by theblades in a group.

The number represented by m is a whole number,l it is neither equal tonor a multiple of n, and it is preferably equal to n-1. If m is equal ton-l, then the above equation becomes Assuming that n=3 (3 blades persegment) and to blades having high frequencies of vibration,

nevertheless, the first moving blade row of an initial Curtis stage, themoving row o! an initial Bateau stage, possibly the second moving row ofthat the moving blade pitch p1 is 1.20 inches, a stationary vane ornomle pitch p of 1.80 inches may be used and blade vibration, due toirregularities in ow caused by the presence of the vanes, is effectivelyresisted or avoided.

Referring to Fig. 2, it will be noted that the vane pitch and the bladepitch are related so that two vane passages supply three blade passages;and that,inthisview,misequaltothe number ot nozzle passages i0 coveredby the any short blade bladesotagroup ,tbatisnnisequalto2.

Having conceived of the possibility of disturbances making themselvesfelt on the blades as they pass the nozzle jets and of vibration or adangerous resonant condition which might be built up, tests have shownthe existence of such disturbances and the effects thereof. Furthermore,tests show the degree of disturbance, that is, up to the criticalpressure ratio, the pressure ratio necessary for acoustic velocity, theinuence of the wakes behind the nozzle vanes is not very important `butit becomes of increasing consequence as the pressure ratio is furtherincreased.

While the invention is shown as applied to two forms of turbine stages,it will be obvious to those skilled in the art that it is not solimited, but is susceptible of various other changes and modificationswithout departing from the spirit thereof, and it is desired, therefore,that only such limitations shall be placed thereupon as are specificallyset forth in the appended claims. I

What is claimed is:

. 1. In a turbine stage comprising stationary vanes, moving blades eachhaving such natural frequency as to be likely to be resonant with Ielastic fluid flow disturbances due to the presence of the vanes, andmeans for connecting together in groups' the blades of the rst movingrow of the stage; the vane pitch, the blade pitch and the number ofblades connected together in each group having the relation,

where p is the vane pitch, pi the blade pitch, n the number of bladesconnected together in each group, and m is a whole number which isneither equal to nor a multiple of n.-

2. In an arrangement for resisting moving .blade vibration of an elasticfluid turbine initial where p is the vane pitch, p1 the blade pitch, nthe number of blades connected together in each group, and m is a wholenumber which is neither equal to nor a multiple of n.

3. In a turbine stage comprising stationary vanes,A moving blades eachhaving such natural frequency as to be likely to be resonant withelastic uid :dow disturbances due to the presence of the vanes. andmeans for connecting together in groups the blades of the first movigrow of the stage; the vanepitch, the blade pitch and the number ofblades connected together in each group having the relation,

where p is the vane pitch, 1n is the blade pitch. A

and n is the number of blades connected together in each group.

4. In an arrangement for resisting moving blade vibration of an elasticiluid turbine initial impulse stage having the elastic iluid pressureratio thereacross suiiicient to produce elastic iluid velocity' which isacoustic or greater, said initial stage comprising stationary vanes andmoving blades, the individual moving blades having such naturalfrequency as to b likely to'be resonant with elastic iiuid flowdisturbances due to the presence of the vanes, and means for connectingtogether in groups the blades of the moving row of the stage; the vanepitch, the blade pitch and the number of blades connected togeth'er ineach group having the relation,

where p is the vane pitch, p1 is the blade pitch, and n is the number ofblades connected together in each group.

5. In an arrangement for resisting moving blade vibration of an elastichuid, turbine initial impulse stage comprising a row of stationary vanesproviding vane passages, a row of moving blades providing blade passagesreceiving elastic iiuid issuing from the vane passages, the individualmoving blades having such natural frequency as to be likely to beresonant with elastic iiuid flow disturbances due to the presence of thevanes, said vanes and blades being spaced circumferentially so that theblade pitch is twothirds of the vane pitch, and means for connecting theblades together in groups of three.

' REINOUT P. KROON. y

